2,486 research outputs found
Three-sublattice Skyrmion crystal in the antiferromagnetic triangular lattice
The frustrated classical antiferromagnetic Heisenberg model with
Dzyaloshinskii-Moriya (DM) interactions on the triangular lattice is studied
under a magnetic field by means of semiclassical calculations and large-scale
Monte Carlo simulations. We show that even a small DM interaction induces the
formation of an Antiferromagnetic Skyrmion crystal (AF-SkX) state. Unlike what
is observed in ferromagnetic materials, we show that the AF-SkX state consists
of three interpenetrating Skyrmion crystals (one by sublattice), and most
importantly, the AF-SkX state seems to survive in the limit of zero
temperature. To characterize the phase diagram we compute the average of the
topological order parameter which can be associated to the number of
topological charges or Skyrmions. As the magnetic field increases this
parameter presents a clear jump, indicating a discontinuous transition from a
spiral phase into the AF-SkX phase, where multiple Bragg peaks coexist in the
spin structure factor. For higher fields, a second (probably continuous)
transition occurs into a featureless paramagnetic phase.Comment: 8 pages, 8 figure
Field induced multiple order-by-disorder state selection in antiferromagnetic honeycomb bilayer lattice
In this paper we present a detailed study of the antiferromagnetic classical
Heisenberg model on a bilayer honeycomb lattice in a highly frustrated regime
in presence of a magnetic field. This study shows strong evidence of entropic
order-by-disorder selection in different sectors of the magnetization curve.
For antiferromagnetic couplings , we find that at low
temperatures there are two different regions in the magnetization curve
selected by this mechanism with different number of soft and zero modes. These
regions present broken symmetry and are separated by a not fully
collinear classical plateau at . At higher temperatures, there is a
crossover from the conventional paramagnet to a cooperative magnet. Finally, we
also discuss the low temperature behavior of the system for a less frustrated
region, .Comment: revised version - accepted for publication in Physical Review B - 12
pages, 11 figure
Quantum disordered phase on the frustrated honeycomb lattice
In the present paper we study the phase diagram of the Heisenberg model on
the honeycomb lattice with antiferromagnetic interactions up to third neighbors
along the line that include the point , corresponding
to the highly frustrated point where the classical ground state has macroscopic
degeneracy. Using the Linear Spin-Wave, Schwinger boson technique followed by a
mean field decoupling and exact diagonalization for small systems we find an
intermediate phase with a spin gap and short range N\'eel correlations in the
strong quantum limit (S=1/2). All techniques provide consistent results which
allow us to predict the existence of a quantum disordered phase, which may have
been observed in recent high-field ESR measurements in manganites.Comment: 4 figure
Metastable and scaling regimes of a one-dimensional Kawasaki dynamics
We investigate the large-time scaling regimes arising from a variety of
metastable structures in a chain of Ising spins with both first- and
second-neighbor couplings while subject to a Kawasaki dynamics. Depending on
the ratio and sign of these former, different dynamic exponents are suggested
by finite-size scaling analyses of relaxation times. At low but
nonzero-temperatures these are calculated via exact diagonalizations of the
evolution operator in finite chains under several activation barriers. In the
absence of metastability the dynamics is always diffusive.Comment: 18 pages, 8 figures. Brief additions. To appear in Phys. Rev.
Magnetization plateaux and jumps in a frustrated four-leg spin tube under a magnetic field
We study the ground state phase diagram of a frustrated spin-1/2 four-leg
spin tube in an external magnetic field. We explore the parameter space of this
model in the regime of all-antiferromagnetic exchange couplings by means of
three different approaches: analysis of low-energy effective Hamiltonian (LEH),
a Hartree variational approach (HVA) and density matrix renormalization group
(DMRG) for finite clusters. We find that in the limit of weakly interacting
plaquettes, low-energy singlet, triplet and quintuplet states play an important
role in the formation of fractional magnetization plateaux. We study the
transition regions numerically and analytically, and find that they are
described, at first order in a strong- coupling expansion, by an XXZ spin-1/2
chain in a magnetic field; the second-order terms give corrections to the XXZ
model. All techniques provide consistent results which allow us to predict the
existence of fractional plateaux in an important region in the space of
parameters of the model.Comment: 10 pages, 7 figures. Accepted for publication in Physical Review
Spin-phonon induced magnetic order in Kagome ice
We study the effects of lattice deformations on the Kagome spin ice, with
Ising spins coupled by nearest neighbor exchange and long range dipolar
interactions, in the presence of in-plane magnetic fields. We describe the
lattice energy according to the Einstein model, where each site distortion is
treated independently. Upon integration of lattice degrees of freedom,
effective quadratic spin interactions arise. Classical MonteCarlo simulations
are performed on the resulting model, retaining up to third neighbor
interactions, under different directions of the magnetic field. We find that,
as the effect of the deformation is increased, a rich plateau structure appears
in the magnetization curves.Comment: 7 pages, 8 figure
Anharmonic effects in magnetoelastic chains
We describe a new mechanism leading to the formation of rational
magnetization plateau phases, which is mainly due to the anharmonic spin-phonon
coupling. This anharmonicity produces plateaux in the magnetization curve at
unexpected values of the magnetization without explicit magnetic frustration in
the Hamiltonian and without an explicit breaking of the translational symmetry.
These plateau phases are accompanied by magneto-elastic deformations which are
not present in the harmonic case.Comment: 5 pages, 3 figure
Topological phase transition driven by magnetic field and topological Hall effect in an antiferromagnetic skyrmion lattice
The topological Hall effect (THE), given by a composite of electric and
topologically non-trivial spin texture is commonly observed in magnetic
skyrmion crystals. Here we present a study of the THE of electrons coupled to
antiferromagnetic Skyrmion lattices (AF-SkX). We show that, in the strong Hund
coupling limit, topologically non-trivial phases emerge at specific fillings.
Interestingly, at low filling an external field controlling the magnetic
texture, drives the system from a conventional insulator phase to a phase
exhibiting THE. Such behavior suggests the occurrence of a topological
transition which is confirmed by a closing of the bulk-gap that is followed by
its reopening, appearing simultaneously with a single pair of helical edge
states. This transition is further verified by the calculation of the the Chern
numbers and Berry curvature. We also compute a variety of observables in order
to quantify the THE, namely: Hall conductivity and the orbital magnetization of
electrons moving in the AF-SkX texture.Comment: 6 pages, 5 figure
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